BSNL 3G data card is very good in terms of speed, coverage, and cost. This is applicable in Tamil Nadu Circle. But the service in Chennai Circle is worst upto the core. Chennai is a big and a capital city, but even there is no proper 3G coverage, even in main areas like Adyar, T Nagar, etc.
Even if you address the problem to any higher authority, there wont be any response.But Tamil Nadu circle is doing good and has a very good coverage in most of the districts. Only some towns are exceptions.
Service is poor at lower level but awesome if addressed to top level authorities.